Problem: If $x \circledcirc y = 4x-y$ and $x \bigtriangledown y = 2x-4$, find $(5 \bigtriangledown -2) \circledcirc 4$.
First, find $5 \bigtriangledown -2$ $ 5 \bigtriangledown -2 = (2)(5)-4$ $ \hphantom{5 \bigtriangledown -2} = 6$ Now, find $6 \circledcirc 4$ $ 6 \circledcirc 4 = (4)(6)-4$ $ \hphantom{6 \circledcirc 4} = 20$.